The invention relates generally to shift assemblies for transfer cases and more specifically to a single actuator shift assembly for a transfer case which sequences selection and operation of both a two-speed gear reduction assembly and modulating clutch.
In the majority of four-wheel drive vehicles, particularly pickup trucks and sport utility vehicles (SUV""s), a transfer case is utilized to provide drive torque to a secondary vehicle driveline in response to operator inputs and automatic, adaptive drive systems. Such transfer cases may include (1) a center differential which allows speed differences between the primary and secondary drivelines, (2) a clutch which may either inhibit differentiation of a center differential, if the transfer case is so equipped, as noted above, or provide drive torque from the primary driveline to the secondary driveline if the transfer case lacks a center differential and (3) a speed reduction assembly, typically a planetary gear mechanism, to provide a low or reduced speed operating mode when it is engaged in addition to a high speed or direct drive operating mode.
Both the modulating clutch and the speed reduction assembly require an operator or actuator of some type to select and engage them in accordance with the operator""s desire or the command of an automatic, adaptive drive system as noted above.
Various speed reduction assembly actuators are disclosed in U.S. Pat. Nos. 5,878,624 and 6,173,624 co-owned by the assignee. U.S. Pat. No. 5,407,024 discloses both a range selection actuator and a ball ramp friction pack clutch operator.
Other transfer cases such as those disclosed in U.S. Pat. Nos. 5,330,030 and 5,363,938 have utilized a single actuator to effect both speed range selection and clutch engagement. In the latter two patents, an electric actuator provides both speed range selection and activation of a friction clutch pack. However, operating force for the clutch pack is generated through a cam and second class lever arrangement which requires that the electric actuator generate significant operated energy. Generation of such energy suggests that both the size of the actuator and its power consumption will be significant. This, in turn, suggests that improvements in single actuator transfer cases are both desirable and possible.
A shift assembly for a two-speed transfer case utilizes a single actuator to drive both the gear or speed range selection mechanism and a modulating friction clutch pack which selectively transfers drive torque from a primary transfer case output to a secondary transfer case output. The shift assembly includes an actuator which rotates a shift rail and cam having an intermediate helical track and a dwell region at each end. A lost motion assembly operating in conjunction with the helical cam selectively engages and disengages the friction clutch pack when the cam follower is in one of the two dwell regions. Thus, the shift assembly provides sequential operation from full clutch engagement in a first speed range through clutch disengagement in the first speed range, de-selection of the first speed range and selection of neutral, de-selection of neutral and selection of the second speed range and thence increasing engagement, up to full engagement, of the friction clutch pack in the second speed range. If desired, the transfer case may include an interaxle differential.
Thus, it is an object of the present invention to provide a transfer case having a two-speed gear reduction assembly and a modulating clutch which are both controlled by a single actuator assembly.
It is a further object of the present invention to provide a two-speed transfer case having a modulating clutch with a single actuator shift mechanism which sequences clutch engagement, clutch disengagement and selection of a desired speed range and neutral.
It is a still further object of the present invention to provide a transfer case having a two-speed gear reduction assembly, interaxle differential and modulating clutch having a single actuator for sequentially controlling selection of a speed range and engagement of the modulating clutch.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature.